Electrodeposition of low stress ruthenium alloy

ABSTRACT

THICK ELECTRODEPOSITES OF RUTHENIUM ALLOY CAN BE OBTAINED BY ADDING AN ELEMENT OF GROUP III-A OF THE PERIODIC TABLE. THE DEPOSITES OBTAINED ARE PRIMARILY CHARACTERIZED BY THEIR LOW STRESS AND ABSENCE OF SURFACE CRACKS AT THICKNESS UP TO ABOUT 10 MILLIMICRONS.

United States Patent 3,692,641 ELECTRODEPOSITION 0F LOW STRESS RUTHENIUM ALLOY Salvatore Losi, Geneva, Ren Henzi, Carouge, and Andr Meyer, Grand-Saconnex, Switzerland, assignors to Sel- Rex Corporation, Nutley, NJ.

No Drawing. Filed Mar. 22, 1971, Ser. No. 126,886 Claims priority, application Switzerland, Mar. 20, 1970, 4,235/ 70 Int. Cl. (32% 5/32 US. Cl. 204-43 Claims ABSTRACT OF THE DISCLOSURE Thick electrodeposits of ruthenium alloy can be obtained by adding an element of Group III-A of the Periodic Table. The deposits obtained are primarily characterized by their low stress and absence of surface cracks at thicknesses up to about 10 millimicrons.

SUMMARY OF THE INVENTION The present invention concerns the electrodeposition of ruthenium-base alloys and more particularly the codeposition of ruthenium, at least one metal of Column III-A of the Periodic Table and at least one other metal of the platinum family which results in the formation of deposits of superior quality and highly resistant to corrosion.

The invention also relates to the electroplating solutions or baths for carrying out such electrodeposition and to the use of said baths for the plating of conducting articles and work-parts.

BACKGROUND OF THE INVENTION Electroplating aqueous baths for the deposition of ruthenium and ruthenium alloys are known that contain the ruthenium as water soluble derivatives, e.g. the hydrobromide (see for instance British Pat. No. 1,108,051). These baths have been operated at various temperatures and current densities; however, deposition rates and cathode yields were very low and such plating baths have furnished generally highly strained ruthenium deposits. The stress which was present generally caused the formation of cracks in the deposits when the thickness was greater than 1.5 to 2.5 p.111. This and the low energetic yields represent an "important drawback in most industrial applications; for instance for the manufacture of corrosion resistant electrodes, thicker deposits are required with no visible cracks or other faults.

It is an object of the present invention to provide a bath for electroplating ruthenium in the form of an alloy with at least one metal of Group IIIA and at least one other noble metal.

It is also an object of the present invention to provide a bath for electroplating ruthenium in the form of an alloy having increased resistance to corrosion by acids, alkalis, oxidizing agents and anodic electrodissolution in electrolytes, for instance for manufacturing insoluble and corrosion resistant electrodes.

It is a further object of the present invention to provide a bath for electroplating ruthenium in the form of an alloy with at least one metal of Column III-A and at least one noble metal for making deposits devoid of cracks or other defects visible with the naked eye with thicknesses of at least 2.5 ,um. Y

Patented Sept. 19, 1972 "ice DESCRIPTION OF THE INVENTION AND OF THE PREFERRED EMBODIMENTS It has been discovered that the physical aspect and properties and the corrosion resistance of ruthenium-base deposits comprising at least one other metal of the platinum family can be greatly improved by the co-deposition with the above alloy of at least one metal of Group III-A of the Periodic Table. Of particular interest is the fact that thicker crack-free deposits can be obtained.

As used in this specification and in the appended claims, the term ruthenium alloy means an alloy of, at least, ruthenium and a platinum metal. The term platinum metal means a metal selected from the group consisting of rhodium, palladium, platinum, osmium, and irridium.

The electroplating bath of this invention comprises about 0.5 to 50 g./l. of ruthenium, preferably about 2 to 25 g./1. of ruthenium, as the complex at least one metal of Column III-A of the Periodic Table in the form of a water soluble compound in an amount from about 0.01 g. metal/l. to the saturation concentration of said water soluble compound in the bath, preferably from about 1 g./l.; and at least one other metal of the platinum group in the form of a water soluble compound in concentrations from about 0.05 to 20 g. metal/1., preferably about 0.10 to 10 g. metal/l.

The preferred Group III-A metals are indium, gallium and thallium. The preferred platinum metals are rhodium, palladium and platinum.

The water soluble compounds of Group III-A metals and platinum metals can be the salts of said metals with most common strong organic and inorganic acids such as for instance sulfuric acid, phosphoric acid, hydrogen halide (chloride and bromide), perchloric acid, tn'chloracetic acid, trifluoracetic acid and the like. Said compounds can also be the water soluble complex chelates of the ions of the above metals with usual metal chelating agents.

The electrodeposits of ruthenium alloys obtained with the baths of the invention are shiny, corrosion resistant and more ductile than other ruthenium alloy deposits obtained previously. Maximum thicknesses of about 2.5 un. can be attained without the metals of Column III-A whereas thicknesses of 10 m. or more can be attained with the co-deposition of Column IIIA metals before the formation of cracks becomes visible with the naked eye or with 500 fold magnification. The use of the bath also leads to other improvements such as for instance faster deposition rate, better cathode yield and better microand macro-distribution of the plated metals over the ruthenium plating baths known previously.

The baths of the invention can be used to plate a great variety of objects, parts, articles and work-pieces which are either self-conductors of electricity (metallic items) or rendered conductors by the application of a conduct- The simultaneous presence in the bath of the invention of ruthenium, one metal of Column III-A, e.g. indium, and one platinum metal has the following additional consequence; the ruthenium content of the deposits can be varied as a function of the concentration ratio of ruthenium to indium, said content being decreased with decreasing ratio of ruthenium to indium.

Temperature, current density, pH and other operating conditions are relevant only as far as they influence the basic characteristics of the plating bath in a known manner. Thus, operating conditions commonly employed with conventional ruthenium plating solutions may be employed in the practice of this invention.

The baths are generally operated at current densities between about 0.1 and 40 a./dm. and preferentially between about 0.5 and 4 a./dm.

The baths are generally operated at a temperature between 15 and 95 C. It is preferred however, to operate between 40 and 70 C.

The pH of the baths is preferably maintained at 3.0, or below, most preferably 1.5 or below. If necessary, the pH is adjusted with acids such as for example HCl, H SO H PO sulfamic acids, benzene sulfonic acids or salts which might have a buffering action in the bath, e.g., NaH PO or Na HPO or salts of strong acids and weak bases.

So as to produce a better adherence and for limiting the formation of porous deposits, it is advantageous, in some cases, to apply a flash of gold on the support before the electrodeposition of the ruthenium alloy.

The weight percent of ruthenium, platinum metal and Group III-A metal in the electrodeposit will vary depending upon the composition of the particular electroplating solution used. In general, the amount of ruthenium in the deposit ranges from about 20 to 80%, preferably from about 30 to 75%; the amount of platinum metal ranges from about 15 to 75%, preferably from about 25 to 70%; and the Group III-A metal ranges from about 0.1 to 10%, preferably from about 0.5 to 5%.

The following examples serve only to illustrate the invention in a more detailed manner, and are not meant in any way to be limitative.

EXAMPLE 1 \An electroplating bath for deposition of a rutheniumbase alloy was prepared by mixing the following ingredients (the concentrations of the metal salts or complexes are given in g. of free metal).

The bath was adjusted to pH 2.0 with 20% ammonia, then it was operated at 1.0 a./dm. and 55 C.

Gold plated brass samples were plated for various periods. The deposits obtained (A) were shiny, with no cracks discernible with the eye or the microscope with thickness up to ,um. The plating rate was 12 mg./a.min., i.e. 0.1 pJJL/ min. The alloy contained 66% Ru, 33% and 1% indium.

In another experiment the above bath without indium was operated in the conditions described above.

Deposits containing 67% Ru and 33% Rb were obtained with thicknesses at least 2.5 #111. before cracks which were visible with an enlargement of 500 fold or with the eye started to appear.

In a control experiment, the above bath without rhodium was operated in the condition described above and gave deposits of Ru plus In (B). A corrosion test was set up as follows: The samples (A) or (B) were used as anodes in an electrolyte containing 20 g./l. of citric acid and 25 g./l. of NaOH. The electrolysis was carried out for 20 h. at 20 C. The anodes were weighed and the losses of deposits were for A 0.008 mg./cm. .a.h. and for B 0.05 mg./cm. .a.h. A was shiny with no trace of corrosion; B was shiny but showed several corroded spots.

EXAMPLE 2 An electroplating bath for the deposition of rutheniumbase alloy has been prepared as described in Example 1 but with 2 g./l. of rhodium metal as the sulfate instead of 1 g./ 1. The bath was operated as described in Example 1.

Deposits containing 40% Ru, 59% Rh and 1% indium were obtained. As in Example 1, they showed no cracks or other defects even with thicknesses of up to 10 ,am.

A control bath with no indium was run as a matter of comparison in the same conditions as above. The deposits behaved as in the second experiment of Example 1.

A corrosion control experiment carried out as described in Example 1 showed that the above deposit with 59% Rh were even more corrosion resistant than the 33% Rh deposit, when it Was used as an anode in an alkaline electrolytic bath.

EXAMPLE 3 An electroplating bath for the deposition of a ruthenium-base alloy was prepared by mixing the following ingredients (the concentrations of the metal salts or com plexes are given in g./1. of free metal).

Ingredients: G./l. (NH4)3RU2CI3(HZO)ZN Na PtCl 0.2 Indium sulfate 5.0 Ammonium sulfamate 20.0

The bath was adjusted to pH 1.5 and operated at 1.0 a./dm. at 6 5 C. The samples were prepared as described in Example 1 and the cathode-yield was 8 mg./a.min. The samples were shiny and had good corrosion resistance.

EXAMPLE 4 An electroplating bath was prepared as described in Example 3 but replacement of the platinum by 0.05 g./l. of palladium in the form of a HCl solution of PdClg- The conditions of operation were the same as for Example 3. Corrosion resistant deposits were obtained at a rate of 9.4 mg./a.min.

We claim:

1. An aqueous acid electroplating bath for the electrodeposition of ruthenium alloy said bath comprising about 0.5 to 50 g./l. of ruthenium, as the complex at least one metal selected from indium, gallium, or thallium in an amount from about 0.01 g. metal/l. to saturation; and at least one other platinum metal in an amount from about 0.05 to 20 g. metal/l.

2. The bath of claim 1 wherein the platinum metal is rhodium, palladium or platinum.

3. The bath of claim 2 wherein the pH is 3.0 or below.

4. The bath of claim 3 wherein the Group III-A metal is indium.

5. The bath of claim 3 wherein the Group III-A metal is gallium.

6. The bath of claim 2 wherein the pH is 1.5 or below.

7. A method of electrodepositing a low stress ruthenium alloy which comprises passing a current through the aqueous acid bath of claim 1.

8. The method of claim 7 wherein the platinum metal is rhodium, palladium or platinum.

9. The method of claim 8 wherein the pH of the bath is maintained at 3.0 or below.

10. The method of claim 8 wherein the pH of the bath is maintained at 1.5 or below.

References Cited UNITED STATES PATENTS 6 OTHER REFERENCES Frederick A. Lowenheim: Modern Electroplating,

Meyer 204 43 P- 6 Zlmmermann et 204-47 6 GERALD L. KAPLAN, Primary Examiner Blake 204-47 Benham 204-43 US. Cl. X.R. Tyrrell 204-43 75-172 

